US missile attack on Syria in 'vital national security interest' - Trump

He said the strike was in the "vital national security interest", adding that the US must "prevent and deter the spread and use of deadly chemical weapons".

Britain led international support for the attack, describing it as a "limited and appropriate" response to the actions of President Bashar Assad's forces.

Defence Secretary Sir Michael Fallon said the Government had been in "close contact" with the US administration in the run-up to the strike.

However the action was angrily condemned by Russia - Assad's principal international backer - as an "aggression against a sovereign state in violation of international law".

President Vladimir Putin's spokesman Dmitry Peskov said in statement carried by Russian news agencies that the US had acted under a "far-fetched pretext".

The Syrian military said at least six people were killed and several others injured in the strike on the base at Sharyat, in central Syria, from where Tuesday's chemical strike was believed to have been launched.

The surprise barrage of 59 cruise missiles in the early hours of Friday, UK time, was the first direct US attack on the Syrian government.

Mr Trump said he was responding to the attack on the rebel-held town of Khan Sheikhoun that killed at least 72 people, including 20 children, which he said was launched by the regime.

Speaking from Florida, Mr Trump announced his strike in an emotional message to the public in which he evoked images of children dying.

"Using a deadly nerve agent, Assad choked out the lives of helpless men, women and children. It was a slow and brutal death for so many," he said.

"Even beautiful babies were cruelly murdered in this very barbaric attack.

"Tonight, I ordered a targeted military strike on the airfield in Syria from where the chemical attack was launched.

"It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons.

"There can be no dispute that Syria used banned chemical weapons."

A No 10 spokeswoman said: "The UK Government fully supports the US action, which we believe was an appropriate response to the barbaric chemical weapons attack launched by the Syrian regime, and is intended to deter further attacks."

US Tomahawk missiles, launched from two warships in the Mediterranean Sea, targeted airstrips, hangars, control towers and ammunition areas at the base.

Pentagon spokesman Captain Jeff Davis said it succeeded in "reducing the Syrian government's ability to deliver chemical weapons" by severely damaging or destroying aircraft, according to initial indications, he added.

He also said Russian forces were alerted ahead of the strike to minimise casualties at the airfield.

The action marked a dramatic U-turn by Mr Trump, who had previously indicated the US could seek to work with the Assad regime to end the Syrian conflict.

In 2013, when President Barack Obama was contemplating military strikes, he warned "many very bad things will happen" if he went ahead.

Sir Michael told Sky News: "We've been in close contact with the American government over the last couple of days following the gas attack. There have been intensive consultations in London, in Washington and the United Nations.

"The American Defence Secretary called me to discuss the various options early yesterday evening and, once the president had made his decision, then the American Defence Secretary called me again to give us advance notice of the strike and the Prime Minister has been kept informed throughout."

Asked if the unilateral action had caught him by surprise, Sir Michael said: "No, we've seen the first test of the Trump administration here.

"This is the first time it's happened under the Trump administration and they've decided they want to help deter it in future.

"This was a very limited, very appropriate, narrowly-focused action to attack the airfield, the aeroplanes and the equipment that the United States believe was involved in the gas attack to deter the regime from future attacks and hopefully therefore save lives in the future."

Sir Michael added: "This particular action was taken by the United States on their own, they did not ask for our assistance."

Liberal Democrat leader Tim Farron backed the US action and said the UK should be prepared to become involved militarily as well.

He said: "The British Government, rather than just putting out a bland statement welcoming this, should now follow it up and call an emergency meeting of the Nato alliance to see what else can be done, be that more surgical strikes or no fly zones.

"Evil happens when good people do nothing. We cannot sit by while a dictator gasses his own people. We cannot stand by, we must act."

Former Ukip leader Nigel Farage told the Press Association: "I am very surprised by this. I think a lot of Trump voters will be waking up this morning and scratching their heads and saying 'where will it all end?'

"As a firm Trump supporter, I say, yes, the pictures were horrible, but I'm surprised. Whatever Assad's sins, he is secular."

Mr Farage urged Britain not to get involved in any further strikes, saying: "Previous interventions in the Middle East have made things worse rather than better."

Ukip leader Paul Nuttall said: "The whole world rightly condemns the use of chemical weapons in Syria, but the US attack on the Assad regime does nothing to lower tensions, nor will it hasten peace in that country.

"Too often rash responses to horrific situations are about the conscience of the attacker, rather than a clear-headed response to an awful situation.

"There are currently no good options in Syria. Assad or Isis is not a choice anyone would wish to make. But firing off missiles in an enraged response shows weakness not strength in the face of horror.

"I hoped for better from this administration."

Jonathan Bartley, co-leader of the Green Party, said: "We absolutely condemn what Assad has done and all of us woke up to see those pictures a few days ago of women and children being killed in a vile chemical attack

"But I think everybody agrees there is no simple solution, no simple pathway to peace, there are proxy wars going on."

He added: "The response of Donald Trump has been to launch these military strikes and we don't think that is part of any coherent plan to bring peace to the situation and it risks actually making the situation worse.

"We have to look at this in the long term.

"Of course those chemical attacks were vile but bombing isn't the answer."